ABSTRACT:

This Paper describes the seismic design of the Sakhalin offshore installations with emphasis on the method used to provide seismic isolation between the Concrete Gravity Base Substructure (GBS) and topsides. The method is based on use of Friction Pendulum Bearings. Each deck uses four such bearings, placed at each support point of the integrated deck, between the deck and GBS. The Pendulum Bearing comprises two low-friction, spherical surfaces, which slide relative to each other, thereby enabling relative movement between GBS and topsides. The friction factor in the FPB is typically 4-6% and stays reasonably constant over the lifetime of the installation. The displacement capacity of the FPBs (700mm) and the load carrying requirement is such that these bearings are among the largest ever made. One important aspect of this design is that the components, which span between GBS and topsides, in particular risers and conductors, need to accommodate the horizontal movement of the topsides over the friction pendulum bearings. The paper demonstrates that use of FPBs for these structures has provided a very effective means of providing seismic isolation, resulting in a highly reliable seismic design.

INTRODUCTION

Sakhalin Energy Investment Co (SEIC) with Shell as operator is currently developing two fields offshore Sakhalin (Lunskoye and Piltun). The development includes construction of two offshore production platforms, pipelines to shore, onshore processing facilities, onshore oil and gas pipelines to Aniva Bay on the South side of Sakhalin Island and a facility for conversion of gas to LNG for export. Production from these two fields is planned to reach 160,000 barrels per day of oil and 9.4 million Tonnes of LNG per year, making it one of the largest LNG plants in the world. Total capital expenditure is estimated at US$12.0 billion.

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